Some thoughts + problems after using the physics stuff

cocos2d-x C++
1

1. Why the use both Vec2 and std::vector< Vec2 >?

consider this code to trace an image and use the points to create a polygon:

auto ap = AutoPolygon("images/tst.png");
auto rect = Rect(0, 0, 300, 300);
std::vector<Vec2> ptLst = ap.trace(rect);

Vec2* ptsAry = new Vec2[ptLst.size()];

for (size_t i = 0; i < ptLst.size(); i++)
	ptsAry[i] = ptLst.at(i);

auto bottleBody = PhysicsBody::createEdgePolygon(ptsAry, ptLst.size());
bottleBody->setDynamic(true);
	
auto bottle = Node::create();
bottle->setPhysicsBody(bottleBody);

delete [] ptsAry;

trace() returns a vector; createEdgePolygon (as well as createEdgeChain and createPolygon) wants a Vec2*. In order to prepare that Vec2* I need to create that array, pick up the points I got from trace() and delete the array when I’m done.
I have two problems with this (assuming I’m doing this right): Cocos2d offers a lot of help in terms of memory management - in form of the Ref class - but here I’m forced to manage my own memory (for array creation/deletion), which kind of feels like an oversight. And also… why not just have createEdgePolygon take a std::vector - or any iterable class, I guess?

PhysicsBody::createEdgePolygon(const std::vector<Vec2> points, int count, ...

2. BodyTypes
The physicsBody class has a function called setDynamic, which toggles it between being a DYNAMIC type or a KINEMATIC type, but what about the third body type STATIC, which is what I’d normally use for walls, floors or other inanimate objects? Wouldn’t a

void PhysicsBody::setBodyType(BodyType type);

be a better method for letting the user decide which body type to use?

3. getCPBody() problem
For some reason when I type “myBody->getCPBody()->” I don’t get any auto-completion what so ever, what am I doing wrong?

4. Hmm…

I traced an image and created the above polygon (the floor is set to dynamic = false). When the U-shape falls onto the floor the game crashes and gives me this error:

Assert failed: CCNode#rotation. RotationX != RotationY. Don't know which one to return

File: CCNode.cpp
Line: 301

Expression: _rotationZ_X == _rotationZ_Y

I’ve tried everything I can think of, might have to try to remove that assert, but will that break something else for me later on?

5. Hmm indeed
This is also from a traced image, just a square. It’s drawn diagonally in the source image, but what’s strange is its behaviour. It sways slowly back and forth on one of its corners like a boat until it settles eventually on one of its sides. It’s like its center of gravity was off-screen or something. Anyone know how to fix this?

That’s all I had for now. I’m sure I’ll have more to add later!

2

Can you send me more of a working example to play with when I have some time? You can get it to me privately if you can’t share publicly.

3

it’s not much else to share than what’s in the first post, but here you go.
setup a scene with initWithPhysics(), override onEnter and setup the world and the objects:

auto org = Director::getInstance()->getVisibleOrigin();
auto screen = Director::getInstance()->getVisibleSize();
auto physWorld = Director::getInstance()->getRunningScene()->getPhysicsWorld();
physWorld->setGravity(Vec2(0, -2200));
physWorld->setDebugDrawMask(PhysicsWorld::DEBUGDRAW_ALL);
physWorld->setSubsteps(3);

make the floor - you can use any picture you want.

auto floor = Sprite::create("images/floor.png");
floor->setAnchorPoint(Vec2::ANCHOR_MIDDLE_TOP);
floor->setContentSize(Size(screen.width, floor->getContentSize().height));
floor->setPosition(org.x + screen.width * 0.5, floor->getContentSize().height);

auto floorBody = PhysicsBody::createBox(((Size(screen.width, floor->getContentSize().height))));
floorBody->setDynamic(false);
floorBody->setRotationEnable(false);
floor->setPhysicsBody(floorBody);
addChild(floor);

add traced object. actually made a small improvement so that the array’s memory is handled automatically (unique_ptr).

// only used for getting the image's size when offsetting the body's position
std::unique_ptr<Image> img = std::make_unique<Image>();
img->initWithImageFile("images/tst.png");

auto ap = AutoPolygon(img->getFilePath());
auto rect = Rect(0, 0, img->getWidth(), img->getHeight());
std::vector<Vec2> ptLst = ap.trace(rect);
std::unique_ptr<Vec2*> ptsAry = std::make_unique<Vec2*>(new Vec2[ptLst.size()]);

for (size_t i = 0; i < ptLst.size(); i++)
	(*ptsAry)[i] = ptLst.at(i);

auto bottleBody = PhysicsBody::createEdgePolygon(*ptsAry, ptLst.size());
bottleBody->setDynamic(/*true*/ false);
bottleBody->setPositionOffset(Vec2(-img->getWidth() * 0.5, -img->getHeight() * 0.5));
	
auto bottle = Node::create();
bottle->setPhysicsBody(bottleBody);
bottle->setPosition(org.x + screen.width * 0.5, screen.height * 0.5);

addChild(bottle);

use this img:
tst

that’s it!

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